Multi-channel Cochlear Implant (CI) systems consist of an external headset with a microphone and transmitter, a body-worn or ear-level speech processor with a battery supply, and an internal receiver and electrode array. The microphone detects sound information and sends it to the speech processor which encodes the sound information into a digital signal. This information then is sent to the headset so that the transmitter can send the electrical signal through the skin via radio frequency waves to the internal receiver located in the mastoid bone of an implant recipient.
The receiver sends the electrical impulses to the electrodes implanted in the cochlea, thus stimulating the auditory nerve such that the listener receives sound sensations. Multi-channel CI systems utilize a plurality of sensors or electrodes. Each sensor is associated with a corresponding channel which carries signals of a particular frequency range. Accordingly, the sensitivity or amount of gain perceived by a recipient can be altered for each channel independently of the others.
In recent years, CI systems have made significant strides in improving the quality of life for profoundly hard of hearing individuals. CI systems have progressed from providing a minimal level of tonal response to allowing individuals having the implant to recognize upwards of 80 percent of words in test situations. Much of this improvement has been based upon improvements in speech coding techniques. For example, the introduction of Advanced Combination Encoders (ACE), Continuous Interleaved Sampling (CIS) and HiResolution, have contributed to improved performance for CI systems, as well as other digital hearing enhancement systems which incorporate multi-channel and/or speech processing techniques.
Once a CI system is implanted in a user, or another type of digital hearing enhancement mechanism is worn by a user, a suitable speech coding strategy and mapping strategy must be selected to enhance the performance of the CI system for day-to-day operation. Mapping strategy refers to the adjustment of parameters corresponding to one or more independent channels of a multi-channel CI system or other hearing enhancement system. Selection of each of these strategies typically occurs over an introductory period of approximately six or seven weeks during which the hearing enhancement system is tuned. During this tuning period, users of such systems are asked to provide feedback on how they feel the device is performing. The tuning process, however, is not a user-specific process. Rather, the tuning process is geared to the average user.
More particularly, to create a mapping for a speech processor, an audiologist first determines the electrical dynamic range for each electrode or sensor used. The programming system delivers an electrical current through the CI system to each electrode in order to obtain the electrical threshold (T-level) and comfort or max level (C-level) measures defined by the device manufacturers. T-level, or minimum stimulation level, is the softest electrical current capable of producing an auditory sensation in the user 100 percent of the time. The C-level is the loudest level of signal to which a user can listen comfortably for a long period of time.
The speech processor then is programmed, or “mapped,” using one of several encoding strategies so that the electrical current delivered to the implant will be within this measured dynamic range, between the T- and C-levels. After T- and C-levels are established and the mapping is created, the microphone is activated so that the patient is able to hear speech and sounds in the environment. From that point on, the tuning process continues as a traditional hearing test. Hearing enhancement device users are asked to listen to tones of differing frequencies and volumes. The gain of each channel further can be altered within the established threshold ranges such that the patient is able to hear various tones of differing volumes and frequencies reasonably well. Accordingly, current tuning practice focuses on allowing a user to become acclimated to the signal generated by the hearing device.
The above-mentioned tuning technique has been developed to meet the needs of the average user. This approach has gained favor because the amount of time and the number of potential variables involved in designing optimal maps for individual users would be too daunting a task. For example, additional complications to the tuning process exist when users attempt to add subjective input to the tuning of the hearing enhancement system. Using subjective input from a user can add greater complexity to the tuning process as each change in the mapping of a hearing enhancement system requires the user to adjust to a new signal. Accordingly, after a mapping change, users may believe that their ability to hear has been enhanced, while in actuality, the users have not adjusted to the new mapping. As users adjust to new mappings, the users' hearing may in fact have been degraded.
Tuning methods and systems also have value outside of the cochlear implant or hearing device space, for example, for speech recognition (“ASR”) systems. ASR systems are often incorporated into such technologies as cellular or other phones (in so-called “voicedial” or “speak-to-talk” systems), computer-based speech-to-text software for word processing, voicemail-to-email conversion systems (that send the contents of an audio voicemail in a text email format), and automated phone systems (for example, automated call-in centers for customer service). A tuning system would allow an ASR system to be tuned to match a particular speech model of a user, notwithstanding the ASR system's initial programming, thus making the technology in which the ASR system is incorporated useful for a larger number of users.
Since different people pronounce the same words differently, it is helpful to tune an ASR system to a user's particular speech model. Such tuning allows ASR systems to be modified such that the system perceives an appropriate stimulus, notwithstanding any particular speech model of the person using the ASR system. Returning to the voicedial or speak-to-talk example, if the ASR system contained in the cell phone is initially set at the point of manufacture to recognize stimuli as spoken by a typical speaker, it should operate properly when such a typical speaker (i.e., one that suffers from no speech-related impediment) uses the ASR system. However, if that ASR system is being used by a person with a speech impediment, it may incorrectly recognize certain stimuli, and may dial the incorrect contact or take other inappropriate action.
What is needed is a tuning system that would allow an ASR system to be tuned to match the particular speech model of any user, notwithstanding its initial programming, thus making the device useful for a larger number of users. Research has been performed regarding such systems for tuning ASR systems, but the resulting tuning systems still display performance limitations.